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Figure 2. 24. Load–displacement curves of 6061, 7075 and AlSi7 alloy foams<br />

.(Source: Campana and Pilone 2008)<br />

The strain rate sensitivity of Al foams produced by powder metallurgy route<br />

(IFAM) and gas injection process (CYMAT) was investigated (Zhao, et al. 2006).<br />

Although, IFAM foams showed strain rate enhancement in the mean flow stress by<br />

15%, brittle CYMAT Al foam showed no strain rate sensitivity (Zhao, et al. 2007,<br />

Zhao, et al. 2006). The progressive folding of cell walls was observed in the deformed<br />

IFAM foam (Figure 2.25(a)), while the cells cracked multiply in CYMAT foam (Figure<br />

2.25(b)). The rate sensitivity was proposed to be resulted from the micro inertia of<br />

progressive folding. In the compression testing, the deformation started at the weakest<br />

region in CYMAT foam (Ruan, et al. 2002). Following the densification in the weakest<br />

region, the deformation continued to another weakest region as shown in Figure 2.26.<br />

(a) (b)<br />

Figure 2. 25. a) Progressive cell wall folding in IFAM foam and b) the cell wall<br />

fracture in CYMAT foam (Source: Zhao, et al. 2006).<br />

27

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